In general, Power over Ethernet (PoE), which is outlined in IEEE Std 802.3™-2005 clause 33 (the PoE standard), refers to a technique for delivering power and data to an electronic device via Ethernet cabling. In a PoE system, a power sourcing equipment (PSE) device provides a power supply to electronic devices, which may be referred to as powered devices (PDs), via an input/output (I/O) network interface that couples to an Ethernet cable. An example of such an I/O network interface is an RJ-45 connector. PoE eliminates the need for a separate power source to deliver power to attached powered devices. Such powered devices may include Voice over Internet Protocol (VoIP) telephones, wireless routers, security devices, field devices to monitor process control parameters, data processors, other electronic devices, or any combination thereof.
In general, the PoE standard requires the chassis and data circuitry of the PSE device to be electrically isolated from the I/O network interfaces and from other interfaces that are user accessible, including a metal housing, a display, a touch screen, a switch, a screw, another connector, or any combination thereof. Conventionally, each I/O network interface is isolated from a physical transport circuitry (PHY) by a transformer that provides such electrical isolation. In a system that has multiple I/O network interfaces, a corresponding number of transformers are used to provide isolation. Each transformer adds cost and contributes to the size of the circuit. Hence, there is a need for improved and/or simplified electrical isolation circuitry.